Inertial sensors, such as accelerometers, have wide applications in many industries. Most notable perhaps being in the aerospace, military, and automotive industries. More recently, they may be found in computer video game controllers where the controller senses user body movements.
One type of traditional accelerometer is the mercury switch. Typically this comprises a sealed tube containing a pair of electrodes and a small amount of mercury. When the tube is tilted or the mercury otherwise accelerated it makes contact with the electrodes and completes an electrical circuit. This may be considered a type of one-bit accelerometer; one bit, because it's either on or off. Unfortunately, mercury is toxic and containment may be an issue. Further, such switches are relatively large, and cannot be fabricated by photolithography.
Another type of accelerometer or switch is the spring-post sensor which is based on low spring constant designs. They typically comprise a partially released cantilever moving normal to the surface of an electrode pair, thus varying the transimpedance between the electrodes. Though it can be made robust, this design has inherent problems. The strain at the edge of the anchors of the beam or cantilever is an order of magnitude greater than the average strain in the structure. This repetitive transient strain gradient changes the mechanical properties of the switch, thus altering its switching thresholds as a function of time. Eventually, the edge of the anchor may become weak, and break under mechanical stress.